Cryogenic air separation process is one of the most efficient and preferred technique for generation oxygen, nitrogen and argon in large scale. Air separation using any technique, cryogenic or non-cryogenic, involves filtering, compressing and cooling of the incoming air. Ambient air is compressed to around 5 to 8 bar depending on the desired product. Subsequently, the compressed air is cooled with most of the water vapor in the incoming air is eliminated.
After the compression the next step involves removing impurities from the processed air especially residual water vapors, carbon dioxide and hydrocarbons. For accomplishing it most of the air separation plants use molecular sieves for removal of carbon dioxide and water through adsorption onto the surface of the molecular sieves at room temperature. The adsorbent materials used in the sieves can be
Process for Cryogenic Air Separation and Liquefier Systems
During this process, the incoming air is cooled to low temperature at the warm-end of the heat exchanger freezing water vapors and carbon dioxide on the walls of the heat exchangers. Refrigeration is generated at cryogenic temperature levels in order to make up for the heat leaked into the cold equipment. Refrigeration cycle used in the cryogenic air separation plants is quite similar to the one which used in our home air conditioning systems.
For increasing chilling and plant energy efficiency, the pressure is reduced or increased inside the expander, which is a type of turbine. However, the energy generated in the expander can be used for running any energy consuming machinery such as an oil pump. Low pressure is good for low separation power needs. If oxygen or nitrogen is required at a higher pressure you can use product compressors or any of the cycle options for supplying oxygen or nitrogen. By removing product compressor and its power, the higher delivery pressure processes are considered cost-effective in comparison to separation and compression.
If you need a higher percentage of plant production in the form of a liquid is necessary that a supplemental refrigeration unit is added to the basic air separation plant. The units attached for providing refrigeration are called liquefiers. Their capacity is determined by the estimated daily demand for bulk liquid products and the requirement of generating supplemental liquid for on-site clients served from the same air separation plant. However, the liquefier capacity may range from small percentage of the air separation plant to its entire generation capacity for oxygen plus nitrogen and argon.